This invention relates to a watthour dial register having a clutch mechanism for periodically uncoupling a dial indicator from a rotatable measuring element driven in response to variations of a quantity to be measured.
Dial registers are typically used in various types of meters for indicating the consumption of different quantities to be measured. In electric energy meters, a disk and shaft assembly forms a measuring element that is electromagnetically rotated at the rate of consumption of electric energy. Rotations are coupled by one or more register gear trains to clock type dial pointers which totalize the rotations for indicating kilowatthours of electric energy consumption. When measurements are to be made only during preselected time intervals, for example only during one or more periods of each day, the periodically operated dial pointers must remain uncoupled from the measuring element while it continues to rotate. Also, the dial pointers must be held against movement when uncoupled from the measuring element. The register gear trains often include a shiftable shaft which produces meshing and demeshing of a pair of gears to produce the periodic coupling and uncoupling operations. It has been found that a large number of meshing and demeshing operations provided by the reciprocally movable gear shaft causes errors and inaccuracy in the dial readings. One cause of the errors is that the meshing of a movable gear with a fixed gear gives a tooth-to-tooth error by causing rotation of the movable gear clockwise or counterclockwise as the two gears enter meshing engagement. Further, an axially movable gear will sometimes have its teeth aligned so as to hit the teeth of the fixed gear causing an instantaneous jamming condition and a resulting clockwise or counterclockwise rotation of the gears. Still further inaccuracies are produced when a braking system is used to hold an axially fixed gear train rotationally stationary in the uncoupled condition by introducing undesired gear backlash in the fixed gear train and adding to the aforementioned tooth-to-tooth meshing errors as it is engaged by an axially moving gear. Registers incorporating the aforementioned movable gear design are described in the following U.S. Pat. Nos. 2,139,821; 2,246,185; 2,132,256; 2,830,269; 2,285,882; 2,997,147; and 3,406,338.
Register gear trains of the time-of-day type also may utilize a clutch mechanism to avoid the gear meshing and demeshing error. The clutch mechanism selectively couples and uncouples the periodically operated dial pointer gearing. Many of the prior art register clutch mechanisms produce additional frictional drag or additional rotational torque loading on the rotatable measuring element while the clutch is uncoupled. The mechanical loading on the register gear trains cause them to wear excessively and substantially shorten the operational lifetime of such a register. The substantial variations and loads on the rotatable measuring element during measuring and non-measuring times of the periodically operated dial pointer can cause it to become unstable, produce excessive wear on the disk shaft bearings and substantially reduce the operational lifetime of the measuring element. One example of the aforementioned clutch type of time-of-day or on-peak off-peak type of register is described and claimed in U.S. Pat. No. 4,307,341 and assigned to the assignee of this invention. A clutch mechanism is described in the aforementioned application for watt demand meter registers and includes a clutch driving part continuously driven by a measuring element and the driving part is mounted between a clutch driven part and a clutch closing part which clamps the clutch parts together when the clutch is closed. The present invention is directed to a further improved clutch mechanism which is particularly useful in a time-of-day watthour meter register.